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A Blockchain Double Spend Affects Merchants, Here’s How

True, crypto has been revolutionary. From being labelled as
a threat to traditional but dominant systems to wildfire misinformation that
these digital platforms are conduits for money laundering, the crypto and
blockchain endures.

Well, the community consists of extroverts and are aware that there are more threats to the network that word of mouth. Sometimes it is talked in low tones and was profoundly highlighted by the mysterious Satoshi Nakamoto. Said to be an existential threat, a 51 percent or a double spending attack is a dreaded occurrence.

A while back, Ethereum Classic, a coin so endeared and even
has the prestigious support of CoinBase was “deep chain re-organized”. This reorganization (a
euphemism for a double spend) was striking, news line making and a scary event
for ETC holders. It was because for every double spending event—an event where
one can spend a coin TWICE—or in technical terms use the same inputs of a
broadcasted transaction twice—it means the legitimacy of the network is put in
serious doubts.

On 1/5/2019, Coinbase detected a deep chain reorganization of the Ethereum Classic blockchain that included a double spend. In order to protect customer funds, we immediately paused movements of these funds on the ETC blockchain. Read more here: https://t.co/vCx89dz44m

CoinBase were the first to pick up this attack stating that
the motive was for-profit and not an act of malice from ASIC miners who secure
the network. But here is the misconception when a double spending attack
happens. It is not the coins—in this case ETC—that are stolen. Instead because
perpetrators have an upper hand and control 51 percent of the network’s hash
rate, they can at their pleasure—as long as they have this majority
control—reverse transactions paid in ETC.

Anything you do to harm the dishonest miners who attacked you also harms the honest miners who were trying to protect you. It seems nearly impossible to shed enough of the former without shedding too many of the latter. I'm not convinced an algo change will help.

This means exchanges as well as merchants bear the brunt. And it can be cascading in that double spent coins can be used to hire more hash power from sites as Nice Hash. After that, the same can be used to attack blockchains. It’s easier, Crypto51 rates indicate that Bitcoin Private transactions can be double spent at just $17 per hour.